A number of chemicals have been shown to cause malignant neoplasms in the forestomach of Fischer 344 rats when administered chronically by gavage. The present study was designed to identify early forestomach lesions following two-week repeated gavage administration of some forestomach carcinogens. Groups of 8 or more male F344 rats received one of six reported forestomach carcinogens ethyl acrylate (EtAc), diglycidyl resorcinol ether (DGRE), 1,2-dibromethane (DBE), 1,2-dibromo-3-chloropropane (DBCP), 1-chloro-2-methylpropene (dimethylvinvyl chloride, DMVC), or 3-chloro-2-methylpropene (CMP), one of two structurally related chemicals (methyl methacrylate and dichloroethane) which were negative in chronic carcinogenicity studies or the vehicle (corn oil) alone 5 days/week for 2 weeks. Histopathologic examination of forestomachs of rats sacrificed 24 hr after the last dose indicated no significant difference in the incidence or severity of epithelial cell proliferation in the rat forestomach between the vehicle control group and the two negative control groups. In contrast, the incidence and severity of epithelial cell proliferation of the rat forestomach in every group treated with a forestomach carcinogen was significantly higher than the incidence in the vehicle or negative control groups.